One of the major things that determines the rate of many chemical and physical changes is the amount of surface area where the reaction takes place. For an easy way to see that, you will need:

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A Homemade Barometer

Using common, household materials, we can construct a simple barometer to measure changes in air pressure.

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Have you ever been outside on a clear night, when there was a full moon? If so, you probably noticed that it was incredibly bright, almost ten time brighter than a half moon. How can that be? Shouldn't a half moon be half as bright as a full moon? To find out, you will need:

• a ball, or some other round object
• a lamp or flashlight

The lamp will simulate the Sun, and the ball will simulate the moon. You are going to be the Earth. Lets start with a full moon. Darken the room by turning off the lights, and closing the window shades. Turn on the lamp, and sit with your back to it. Hold the ball out in front of you, so the entire surface of the ball seems well lit. This is how the moon is positioned during a full moon, on the opposite side of the Earth from the Sun. Notice how the light from the Sun (the lamp) is reflecting off the moon (the ball) back to you, making it look very bright.

OK, now lets switch to a half moon, also known as either a first quarter moon or a third quarter moon. To see that, turn in your chair so that the Sun (the lamp) is directly to your left. Again, hold the ball out in front of you. The side of the ball that faces the lamp is still fully lit, but you can only see half of it. The side of the ball that is away from the lamp is dark, and you can see half of that. It should look much like the photograph of the half moon.

Notice that even the lighted part of the ball is not as bright as it was when you simulated the full moon. That is because most of the light is still reflecting back towards the lamp, just as it was before. The difference is that you are not between the lamp and the ball, so that reflected light is not coming towards you.

If you want to compare the actual brightness of the different phases of the moon, do an internet search for "printable eye chart", or make your own. It should have very large letters at the top, and they should get smaller as you go down the page. Print that page, and find a place outside where there are no lights shining on you except for the moon. Notice what phase it is in, and then see how far down the chart you can read, using moonlight for illumination. On a clear night, with a full moon, you should be able to read several of the top lines of letters. A week later, at the half moon, try it again. Be sure that the moon is about the same height in the sky. You will find that it is much harder to see the letters, because there is much less light. You might even try it every night, to see how much it changes from day to day. Does it change the same amount every day? Can you figure out why? Might make a good science fair project.

If you have read many of these experiments, you know that I like experiments that deal with food. Part of this is because I really like to eat. I also like to cook, finding it very relaxing. I also seem to get lots of good feedback from the food related experiments, telling me that many of you like to eat too. This experiment comes from the wonderful dinner we had tonight. Our good friends Bob and James came by today and we went out to eat. I ordered a bucket of steamed oysters (I LOVE oysters!) and I was enjoying dipping them in the various combinations of horseradish, cocktail sauce, and butter. I especially like the clarified butter you get with seafood and that got me thinking about the chemistry butter. To investigate this, you will need:

• at least a couple of tablespoons of butter (not margarine)
• a skillet or sauce pan

Lets start with the history of butter. Butter has been used for a long time. There are references to butter as far back as 2000 BC, although at that time it was used mostly as a medicinal ointment and as oil for lamps. Today, most butter is made from cow's milk, but it has also been made from the milk of goats, sheep, horses and other mammals. There are different ways to make butter, but basically you let whole milk separate so that the cream comes to the top. This cream is then churned or shaken, causing the bits of butterfat in the milk to stick together, forming lumps of butter.

If you want to try that yourself, check out the Making Butter video.

Butter is actually several different substances mixed together. We are going to separate these substances. Cut a couple of tablespoons of butter into small pieces and put them in the pan. Turn the heat on low and watch as the butter melts. You will quickly notice that there are different parts to the butter.

Clear butter fat and white milk proteins

You will see a clear, yellow liquid with lots of white bits floating in it. Continue heating and you will notice that the butter begins to sizzle. At this point, remove it from the heat.

There will be a white foam floating on top of the butter and bits of white, solid stuff will settle to the bottom. In the middle is the yellow liquid. Use a spoon to remove the white foam. You can then carefully pour the yellow liquid into a small container.

boiling the water

Another way to make clarified butter is to place the butter in a small container and place it in a very warm place. The butter will melt and separate into layers. You can then spoon off the foam from the top and carefully pour off the clear, yellow liquid. You don't get the sizzle, so you miss seeing evidence of one of the substances present in the butter, but you also don't need to use the stove.

OK, now what is all this stuff? Well, butter is made up of fat, protein, and water. They form an emulsion, which means that you have a mixture of substances that usually don't mix (oil and water).

Some of the proteins brown,
giving the butter fat a wonderful flavor.

Often, butter has salt and air added to it as well. As you melted the butter, the emulsion separates. The yellow liquid is the fat. The solid, white stuff is the milk proteins. The sizzle of the heated butter was the water boiling away. The foam which forms on top of the butter is mostly due to air that is trapped in the butter during processing.

You can use either salted or unsalted butter in this experiment. If you use salted butter, you need to watch it more closely to keep it from scorching. The salt raises the boiling point of the water in the butter, which means less time between when the water starts to boil and when the proteins begin to burn.

Why do people make clarified butter, which is also known as drawn butter? There are several reasons. First, by removing the solid milk proteins, you can use the butter to cook at much higher temperatures. Regular butter begins to smoke when you heat it to about 248 degrees Fahrenheit. At that point, the proteins begin to scorch, producing a bitter flavor. By removing these proteins, you can heat the clarified butter up to 375 degrees before it starts to smoke. This makes it very useful for cooking food which you want to cook at a high temperature.

The second reason for removing the milk proteins is that it helps keep the butter from spoiling. These proteins are largely responsible for the butter going rancid as it gets old, and properly clarified butter can be kept for a long time without going bad. The better job you do of removing these proteins, the longer the butter will keep.

Now, I can hear some of you asking why isn't all butter clarified. Removing the milk proteins also removes a lot of the flavor. Once it cools, compare the taste of the clarified butter with regular butter and you should taste a big difference. While it tastes marvelous with oysters, lobster and other seafood, it would not have the butter flavor that we like in other foods. Don't waste that clarified butter! If you don't have any oysters or lobster laying around, it is also very good on popcorn. Or heat it again with some garlic, and use it for dipping crispy strips of toasted bread. YUM!

With the holidays upon us, I am once again reading through Michael Faraday's Chemical History of a Candle. You can find it online at http://www.gutenberg.org/etext/14474. Truly a wonderful book. I was trying to think of a new candle experiment and came across a package of the "magic relighting candles" in the birthday card section at the grocery store. These are the ones that relight themselves a few seconds after you blow them out. How do they work? Let's find out. You will need:

• a candle
• a lighter
• one of the self relighting candles

First, lets burn the regular candle. Place it in a secure holder, so it does not fall over. Light the candle and let it burn for a couple of minutes. Check to see that it has formed a nice pool of melted wax around the base of the wick. Then blow out the candle. You should see a column of white smoke rising from the wick. Blow strongly on the wick, and you should see an ember glowing at the end of the wick. That ember and the white smoke are two of the important parts of the relighting candle.

The white smoke is really vaporized paraffin, the stuff the candle is made from. The glowing ember is hot enough to continue vaporizing the paraffin, but not hot enough to set the vapor on fire to relight the candle. That calls for a third ingredient.

Place the relighting candle in a holder. I have found that a cupcake or brownie works very well for this. I also put a little ice cream around it, just for safety. Light the "magic" candle, and let it burn for a few seconds. Then pretend it is your birthday, and blow out the candle. Watch the candle carefully. You should see the same rising column of white smoke. You will probably also see the glowing ember, but do not blow on the wick this time. Instead, watch closely. After a few seconds, the candle relights itself. Just as it relights, you should see something else. There should be tiny, bright sparks that jump from the wick. That is the third thing that we need to have a relighting candle, but what makes the sparks?

The sparks are caused by tiny bits of the metal magnesium. Magnesium is a very light metal. It also burns with a very hot flame. Tiny bits of magnesium are mixed into the wick. While the candle is burning, liquid wax flowing up through the wick keeps the magnesium cool enough not to burn, but once the candle is blown out, the wax cools and stops rising. That lets the glowing ember heat the magnesium bits enough to set some on fire. They burn hot enough to set the paraffin vapor on fire, relighting the candle.

If you relight the candle several times, you will probably get some nice bursts of sparks. Repeated melting can cause some of the particles to concentrate in one place. When they get hot enough, you get a nice, miniature fireworks display.

Once you are done, but sure that the "magic" candle is out. Put it in some water for a little while to be sure. It would not be a good thing to put it into the garbage, and then have it relight again.

Be sure to dispose of the cupcake or brownie properly too, preferably with a little hot fudge sauce and a fork.

To go into this subject deeper, try the following:

The Fire Diamond: To understand what we need to have a fire.

This activity is from my Experiment of the Week Newsletter. It is free, and will let you know about new resources on this site.

This time, we are going to take a look at a classic science experiment that has been used for a LONG time. In fact, it was already an old classic when I was a kid, and that was quite a while ago.

The experiment involves the link between our senses of taste and smell. Often it is done with apples and potatoes, but there is enough textural difference that you can often tell which is which. I have found that the results are much stronger with flavored candy. To try this, you will need:

• candy that has the same shape and texture, but comes in different flavors.

OK, lets begin with the standard experiment. Be sure that your pieces of candy will all feel the same in your mouth, and that they have distinctive flavors. If you don't see the candy, the taste should be your only clue to what flavor it is.

If you have a friend to help, then close your eyes, hold your nose, and have her give you one of the pieces of candy. Keeping eyes and nose tightly closed, put the candy in your mouth. You will taste a sweet taste, and probably some sour too, but you may be surprised that you can't tell if the candy is cherry, lime, orange, or some other flavor.

Then move your hand away from your nose, so you can breath normally. Yum! You get a sudden burst of flavor, telling you exactly what kind of candy it is. The reason for this is that your tongue has flavor receptors for basic flavors, such as sweet, salty, sour, bitter, and umami (the savory taste of meat.) Most of the other flavors that you taste are tied in with your sense of smell. If you can't smell them, then you don't taste them. That is why food tastes so bland when you have a cold.

But wait a minute! Your parents probably taught you to chew with your mouth closed. How can the smell get out of your mouth to go up your nose, so you can smell it? And your mouth stayed closed when you released your nose, but you still got that sudden burst of flavor. What is really happening?

Well, the smell of the food does have to reach your nose for you to taste all of those subtle flavors, but there is another path that those smells can take. Instead of inhaling those smells through your nose, you are exhaling them. As you breath out through your nose, your breath carries the smells from your mouth into your nose. You were not holding your nose to prevent you from inhaling the smells. Instead, you were blocking the way, so you could not exhale the smells through your nose.

Now that you are tasting the flavor, hold your nose again. After a second or two, the flavor disappears again.

So what if you just held your breath instead of holding your nose? Try that.

No, really. Try it and see for your self.

What did you find? Even holding your breath, you probably still tasted some of the flavor. Why? Think about what happens when you chew or swallow. Your mouth changes shape, your throat moves, your tongue moves around. All of that movement causes the air in your throat to move, forcing some of it up into your nose. It carries some of the smell to your nose even if you don't exhale. By blocking your nose, you pressurize it, preventing the air from your mouth from moving up.

OK, take it one more step. Hold your nose until the flavor goes away. Then release your nose, and inhale. While you are inhaling, keep your mouth closed. You probably won't taste the flavor. Then exhale. Ahh, there is the flavor again. The main path that the smells take to let you taste your food is up through the back of your throat. It is not inhaling that brings you the flavor. Exhaling is what gives you those wonderful flavors.

I first became interested in rock stacking during our trip to Technorama, the Swiss Science Center. Thorsten Künnemann, their Executive Director took us on a marvelous tour of Zurich. As we walked along the shore of Lake Zurich, we came to an area that was filled with amazing stacks of balanced rocks. When you first see them, you think that they must be held together with glue or mud. Only when you get very close can you see that it is all a matter of balance. Since then, we have seen similar stacks in other places and made some of our own.

If you would like to try rock stacking, you will need:

• a flat, stable surface
• a variety of rocks or other things to stack
• steady hands
• lots of patience

While at first rock stacking may seem like a frivolous activity, there is actually quite a bit of science and engineering involved. As we saw in the Science of Balance video, we can balance an object by keeping its center of gravity (its balancing point) directly above its base (the part of the object that is supporting it.)

To start, you need a wide variety of rocks, or other objects to stack. If you don't have lots of large rocks, you might try stacking toys, stuffed animals, or other irregularly shaped objects that are not breakable.

Select a large, steady rock as your foundation. You want the rock on the bottom to be very stable, because if it wobbles, your entire stack will wobble, which usually means that it all falls down. By using a wide, flat rock, it has a large base, which gives you plenty of working room to keep the center of gravity inside that base. While you are learning the art of rock stacking, you will have better success if you also choose a foundation rock that has a fairly flat top, to make it easier to balance the next rock.

It is easiest if you start simply, using fairly flat rocks to make stacking easier. Keep in mind that as you add each rock, you are adding pressure to the rocks under it, which may shift their center of gravity. Work slowly. Instead of putting a stone in place and releasing it, gradually let its weight rest on the stack, checking to see whether the stack remains stable.

Once you have the knack of stacking flat rocks, then you can start to get more creative and adventurous. Use rocks with unusual shapes, and try balancing them on smaller bases. Remember that a smaller base means you have to be more careful with the stack's center of gravity. Also remember that each rock can change the center of gravity of the entire stack, throwing the stones below it out of balance. If one orientation is unstable, try turning the rock to a different side. If that does not work, then try a different stone. The more you practice; the more you will learn about the art and science of stacking rocks.

As we saw in the Scavengers and Decomposers video, mushrooms play a major role in the food web as decomposers, breaking down wood and other plant material, and putting some of that energy back into the food web. There are over 14,000 species of mushrooms, and many of them look very similar. We use many different characteristics to identify them, including their shape, their color, their texture, where they grow, and many other things. One important test that can help identify a mushroom is its spore print. Spore prints are easy to make, and some are quite beautiful.

To make a spore print, you will need:

• white paper
• black paper
• one or more mature mushrooms
• scissors or a knife
• clear, acrylic spray (optional)

First you will need some mushrooms. They need to be mature, which means that they have opened fully, often into the shape of an open umbrella. If you don't have any mushrooms growing around your house, you can usually buy them at your local grocery store. You don't want the small, white, button mushrooms. They are not mature yet. Instead, look for the pancake shaped Portabella mushrooms. That is what the button mushrooms would look like if they grew and matured.

Looking at the underside of the mushroom, you may see many thin ridges and grooves radiating from the center. These are the gills. No, they are not used for breathing like the gills of a fish, but they have a similar shape. The gills are where the spores are produced. OK, so what are spores? Spores do much the same job for mushrooms that seeds do for flowering plants. The difference is that mushroom spores are very tiny (You usually need a microscope to see an individual spore.), they don't contain the stored food that seeds have, and they don't have to be pollinated. Each tiny spore is capable of growing into a new mushroom. Not all mushrooms have gills. Some have pores or other openings, but they can still produce spore prints.

If possible, collect two specimens of each type of mushroom. Why? Some mushrooms have white spores, while others have dark colored spores, so for each kind of mushroom, we will put one on white paper and the other on black paper. If the mushroom has white spores, they will be hard to see on the white paper, but will stand out on the black paper. If the spores are dark, then the white paper will make them easy to see.

You want the mushroom to lie flat on the paper, so use scissors or a sharp knife to remove the stem. As you do that, watch closely. Many mushrooms will change color when they are cut or broken. This mushroom was white when it was first cut, but within seconds the cut changed to a dark, rusty red. That color change is another useful trait that can help you identify mushrooms. Not all mushrooms have dramatic color changes, so if you are using a Portabella, you will probably not see much at first, but it will slowly darken.

Place the mushrooms with the gill side down on the sheets of paper. Put them in a place where they will not be disturbed, and let them sit overnight. The spores are so small that even a gentle breeze can carry them away, so if you have a fan or air vent nearby, you should cover the mushrooms with a bowl or a box. As the mushroom sits there, it releases spores, which fall onto the paper.

By the following morning, you will probably be able to see a dusting of spores on the paper at the edge of the mushroom. Very carefully, lift the mushroom off of the paper, being sure not to let it shift or slide. Underneath, you should find a spore print in the shape of the mushroom, usually showing the pattern of the gills.

Different mushrooms form different colored spores. This one had spores that were a very nice green color. You can preserve your spore print by very gently spraying it with a clear, acrylic spray. This spray is often used to protect art projects. Don't hold the spray can too close, as that will blow away many of the spores, and form drips that will mess up your spore print.

On the sheet of paper, write the date and location where the mushroom was collected. You might want to attach a photograph or drawing, and any other information about color changes when cut, texture, shape, etc. If you are able to identify your mushroom, then write its common name and its scientific name on the paper too. You may want to start a collection of mushroom spore prints, and might even decide to become a Mycologist, a scientist who studies mushrooms and other fungi.

Several people have written me lately, asking how to make simulated geodes in egg shells. Geodes are pockets of crystals that form in sedimentary and igneous rocks. They start as hollow spaces in rock that is porous enough for water to seep through. The water carries dissolved minerals, which are deposited in the open space, forming a lining of crystals. Most geodes contain quartz crystals, but they can also contain calcite, celestite, and other minerals.

Many rock shops and museum gift shops sell geodes that have been cut, and sometimes dyed to make them more colorful. Sometimes you can buy unbroken geodes, which lets you break them open yourself. That is particularly fun, as you never know how it will look until you open it.

If you don't have a place to collect geodes, you can make quick, easy, simulated geodes by using egg shells for the hollow spaces. I have seen several different recipes, many of which take days, but you can make an egg shell geode in a few hours by using epsom salts for the crystals. We will be using basically the same formula that we used for Growing Crystals from Solution, so you will need:

• several egg shells, washed and cleaned
• an egg carton to hold the shells
• epsom salts, available at pharmacies and grocery stores
• hot water
• a measuring cup
• a refrigerator
• food coloring

Start by making an omelet or something else yummy that requires eggs. For the best results, crack the eggs close to the small end of the egg. This leaves you a fairly large egg shell to use. The larger the egg shell, the more crystals you will have. Wash the shell, and remove the skin-like membrane that lines the shell. For short term projects, you can leave this membrane in place, but you should remove it if you plan to keep your geode for a long time, as the membrane tends to mold after a while.

Depending on how many eggs you are going to use, you may not need as much of the solution as we used before. I tried using 1/4 cup of epson salts and 1/4 cup of hot water, and it worked fairly well for 6 egg shells. You want the water to be hot, but not boiling. Stir in the epsom salts. If it all dissolves, add another spoon full. Place the egg shells in the egg carton, so they won't tip over and make a mess. Then pour the epson salt solution into the shells.

If you want brightly colored crystals, add a drop of food coloring. You might even try adding small drops of two or more colors to the same shell. Be sure to leave some of them uncolored, because I think the pure crystals are prettier than the colored ones.

Carefully place the egg carton into the refrigerator. Put it in a place where it will not be bumped or disturbed, and let it sit for at least 3 hours. That will give your crystals plenty of time to form.

Once you have plenty of crystals, remove the egg carton from the refrigerator. There will still be liquid in the shells, which you can carefully pour into the sink. Be careful not to let the crystals fall out of the shell as you drain them. Each shell should have a mass of needle-shaped crystals inside. As they dry, they will become even more bright and shiny.

You can play with the concentration of the epson salts. Adding more epson salts to the water will give you a denser cluster of crystals, while adding a bit less will give you a better view of the individual crystals. If you used clean egg shells, your crystals should remain bright and shiny for weeks.

At some time in your life, you have probably heard that in a fall, cats always land on their feet. Is that true? Well, usually it is. Cats have the amazing ability to turn themselves right side up as they are falling. That does not mean that a fall will not injure them. If you fell off a tall building, would landing on your feet keep you from being injured? No. The same is true for cats. Landing on their feet lets their legs flex to absorb some of the impact, and keeps the impact from directly hitting more delicate bones, but cats do not have any magical protection against injury from falling.

What is amazing is the way that they perform this trick of landing on their feet. They do it by combining fast reflexes with the laws of physics. To get an idea of how they do it, you will need:

• a chair that swivels easily. Common office chairs work very well for this.
• an open area with plenty of room, so you don't break any lamps, furniture, or legs.

OK, lets start by thinking about what the cat has to accomplish. It is falling, which means that it does not have anything to push or pull on to turn itself. Instead of falling, you can get an idea of the problem that they face by sitting in the swivel chair. Make sure that you have plenty of open space around you by holding your feet straight out and turning in a complete circle. You want at least a foot or two of open space between your feet and the closest thing you could bump into.

Now lets get an idea of the challenge the cat faces. Sit cross legged in the chair, so your feet do not stick out. Put your arms in your lap, with your elbows tucked in against your side. Your challenge is to turn the chair around so that you are facing the opposite direction by twisting your body from side to side. Don't move your arms or legs. You can twist at the waist and your neck, but nothing else. DON'T HURT YOURSELF! You will find that you can turn the chair slightly to the right by twisting your body to the left. The problem is that when you twist back to the right, the chair spins back to the left, winding up back where it started. Wiggling the chair back and forth is no problem, but you don't get very far towards turning the chair around.

To see how the cat manages its trick, lets try something different. Keep your elbows at your side, but extend your hands out to the side. Then try twisting again. This time you will notice that the same motions cause you to swivel back and forth farther. Extend your arms all the way out, and try it again. Now, you are really moving back and forth. As you move your arms further and farther from your body, you can use their inertia (resistance to changes in motion) to push against.

You still have the problem that you are twisting back and forth. Remember that you are a falling cat, and you need to turn yourself so you can land on your feet. That leads us to your next step.

Extend your arms all the way out, and then twist to your left. That swivels the chair and your body to the right. Now, before you twist the other direction, pull your arms back in close to your body. Since your arms are in close, you can turn back without swiveling the chair back in the other direction. You have turned part of the way around, and you are back into the position to do it again. Extend your arms again, and repeat the process. It took me three arm swings to turn my chair around so that I was facing in the opposite direction.

Cats do this maneuver even better because they are incredibly flexible. They extend their front legs while pulling in their back legs, and then twist in the direction they want to turn. Very quickly, they pull in their front legs, and extend their back legs, making another quick twist that lets them wind up facing as much as 180° from their original direction.

Although cats are incredibly fast at this, it still takes time. Cats that fall from a very short distance do not have enough time to twist around. Also remember that landing on their feet does not mean that they don't get hurt during a fall. Their reflexes and flexibility can help them land in the best position, but they can still suffer injuries and broken bones from a fall; so you should not use your cat as an experimental subject.

If you want to experiment further, try holding a weight in each hand as you do the experiment. Do you think that will make it work better or worse? Try experimenting with different arm motions. I had interesting results from making the same motions that you would use for paddling a canoe.

Link to Penny Chemistry, part 1

Last time, we used a mixture of salt and vinegar to remove the tarnish from pennies. This time, we will get back some of the dissolved copper by collecting it on some iron nails. To try this you will need:

• a small glass, cup, or bowl
• vinegar
• salt
• several pennies
• several iron nails

The start of this experiment is pretty much a repeat of part of last week's experiment. Put a couple of inches of vinegar into a cup. Add a teaspoon of salt, and give it a stir to help it dissolve. This time, instead of dipping a penny halfway into the solution, drop in several pennies.

Very quickly, you will see the same thing happen that we saw last time. The pennies will lose their coating of oxides, becoming bright and shiny. In the process, some of the copper is being dissolved in the vinegar/salt solution.

To get some of that copper back, drop a couple of iron nails into the solution. After a minute or so, you will see tiny bubbles forming on the nails. After an hour or so, look at the nails again. They should have a thin coating of copper.

Why does the copper coat the nails? The solution that dissolved the copper from the pennies is also dissolving some of the iron from the nails. As the atoms of iron dissolve, they leave behind electrons, giving the nail a negative electric charge. Both the iron and copper atoms dissolved in the solution have a positive charge, but the copper is more strongly attracted to the nail, so the copper atoms stick to it, forming a coating.

The bubbles are hydrogen gas, produced by a reaction between the hydrogen ions from the vinegar and the metals. Once enough copper atoms have been deposited to balance out the negative charge on the nail, the process stops.

Does it make a difference if the nail is touching the penny? Try suspending the nail by a string, so it does not touch the copper. Does it still work? To see a stronger contrast, try suspending the nail so that only half is in the vinegar. That part should get a copper coating, while the part above the liquid should remain as it is.

Yesterday's walk on the beaches of New Zealand gave me a great experiment. I was playing with the ironsand, a very heavy, black sand made of titanomagnetite. There is a large deposit of ironsand on the beach at the farm. In trying to sort the different minerals, I was reminded of my gold panning trip to the Carolinas back when I worked at the Memphis Pink Palace Museum, in Memphis, Tennessee. To try your hand at "gold panning," you will need:

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This project has science fair potential.

Way back in the 70's, when I was working at the Memphis Pink Palace Museum, part of our Kitchen Chemistry program involved using packets of ketchup to remove the tarnish from pennies. You take a dull, brown, tarnished penny and rub it with some ketchup. In seconds, the penny is bright and shiny. Usually, the experiment stops there, but I thought we might take a look to see why it works. To try this, you will need:

• ketchup
• water
• vinegar
• salt
• potassium chloride (salt substitute)
• 5 small cups or bowls
• 6 or more tarnished pennies
• labels and a marker

Safety Warning

Before you go wild with pouring different chemicals together, remember to keep safety in mind. For the stuff in your refrigerator and spice cabinet, you can pretty much mix whatever you want. Tuna fish and grape jelly may not be tasty, but it will not explode or burn off your fingers. Outside your refrigerator, you need to be much more careful. Cleaning supplies and other household chemicals can be harmful by themselves, and if the wrong ones are mixed they can be deadly. Only use them for experiments that specifically call for them.

Experiment

A good place to start is with the original experiment. Put a little ketchup onto one of the tarnished pennies. Let is sit there for about 30 seconds, and then rinse it. What you should find is that the tarnish has been removed from the part of the penny that was in the ketchup. OK, so that works just as well as it did back in the 70's.

Next, take a look at the ingredients for the ketchup. Besides tomatoes, you will notice that two prominent chemicals are vinegar and salt. A little internet research will show you many other science experiments that use vinegar and salt for doing the same thing as the ketchup. If you want to be sure that the tomatoes are not responsible for cleaning the pennies, try using some tomato sauce that does not contain vinegar or salt.

After some experimentation, you will probably find that the vinegar and salt are the important ingredients but are they both necessary? Lets find out. Start with four small cups. Put about an inch of water in one. That will be our control. The control does not contain any of the chemicals that we are testing. If it cleans the pennies too that would tell us that the reaction happens, even without the vinegar or salt. Label this cup "Control."

In the second cup, put about an inch of vinegar. Label this one "Vinegar."

In the third cup, put about an inch of water, and then add a teaspoon of salt. Give it a quick stir to dissolve the salt. Label this one "Salt Water."

In the fourth cup, put about an inch of vinegar, and add a teaspoon of salt. Give it a quick stir to dissolve the salt. Label this cup "Vinegar and Salt."

Now, you are ready to do some testing. Lets start with the Control. Dip one of the tarnished pennies halfway into the water, and hold it there for 30 seconds. Remove it from the water, rinse it, and put it beside the Control cup.

Do the same for each of the other cups. Be sure to give each 30 seconds, and be sure to rinse the penny to remove any vinegar or salt. Place each penny beside the solution you used to test it.

Results

OK, now what did you find? If your results were like mine, you found that neither the water, the vinegar, or the salt water did much, if anything to the pennies. The mixture of salt and vinegar was very effective at removing the tarnish.

So what is happening? The tarnish on the penny is copper oxide, and a chemical reaction with the vinegar will actually dissolve it. Then why did the pure vinegar not work? With the penny and the vinegar, you get a series of chemical reactions that form a circle. One reaction removes the copper, but just as quickly, another reaction puts it back. In chemistry, this is known as an equilibrium reaction.

The trick is to add something that will interrupt that equilibrium. You want a chemical that will grab the copper before it can be put back, and the table salt does a very good job of that.

What is it about the table salt that grabs the copper? Table salt is sodium chloride. When you put it in water, it separates into sodium ions (charged atoms) and chlorine ions, but is it the sodium or the chlorine that grabs the copper. An easy way to test that is with a different kind of salt. One of the common salt substitutes is potassium chloride. You can find it beside the regular (sodium chloride) salt at the grocery. In a fifth cup, put about an inch of vinegar and stir in a teaspoon of potassium chloride. Does it work the same as the table salt? If so, then it is the chlorine that grabs the copper. If not, then it is either the sodium, or the combination of sodium and chlorine.

You can look deeper into the vinegar as well. Will it work with other acids? Try using lemon juice (citric acid and ascorbic acid) or carbonated drinks (carbonic acid). Carbonated colas also contain phosphoric acid. Again, remember safety. Look for acids from your refrigerator and spice cabinet, not from other household chemicals.

Link to Penny Chemistry, part 2

In a recent video, we dissected a roast chicken, seeing how the muscles connected to bones to power its wings. This time, we are going to explore a very different arrangement for flight by examining the flight of insects. To try this, you will need: - 2 popsicle sticks or tongue depressors - a hollow, rubber ball - a sharp knife - an adult to use the shape knife (Adults are easier to bandage if they cut themselves.)
Lets start by thinking about bird wings. As we saw in the Bird Bones video, they are made up of several bones, connected at joints, and powered by muscles. An insect's wings are very different. Each wing is all one piece, made of chiton, the same substance that makes its exoskeleton. The wings do not have any joints or muscles. So how do they move?
We can see that by constructing a model, a representation of the insect that will help us understand what is happening. Sometimes scientists use computer models, developing computer programs to simulate a specific event. Other times they construct models from materials to allow them to test ideas. That is what we will do. You need a rubber ball that is hollow, not solid rubber. You can find these in the toy department in many stores. Pick a point on the ball and carefully use the knife to make a cut that is about as long as your popsicle stick is wide. Carefully, insert the end of a popsicle stick into the cut.
Looking at the ball, imagine the face of a clock. Turn the ball until the stick is about at 2:00 on the imaginary clock face. Then make a mark on the ball at about the 10:00 point. Make another cut there, and insert the other stick. Your model butterfly is now complete.
The ball represents the body of the insect. Instead of having muscles attached directly to their wings, most insects move their wings by changing the shape of their bodies. Muscles attach to the top and bottom of the body. Contracting those muscles flattens the body, causing the wings to move up. You can see that by squeezing the ball from top to bottom.
By relaxing those muscles and contracting others, the body changes shape again, moving the wings downwards. You can see that relaxing the hand that is squeezing top to bottom, and instead squeezing the ball from side to side. As the insect flies, its body is flexed by muscles, causing the wings to move up and down. By controlling how much each set of muscles contracts, the insect can change the movement of its wings to control its flight.

This method of flight is used by most insects, including bees, wasps, flies, butterflies, and moths. There are a few insects, most notably Dragonflies and Damselflies, that do have muscles attached to the base of their wings. This lets them control each wing independently, making them very agile fliers.

Link to Whistle Stick, part 1

I hope that you made your own Whistle Stick, and have been playing...., I mean experimenting with it. I also hope that you spent some time thinking about the science behind the sound that it makes, because that is what we are going to explore this time. For your exploration, you will need:

- a wooden spoon
- a large container of water
- the Whistle Stick from last week

It's always good to start with the basics, so begin by thinking about sounds in general. We hear a sound because of waves traveling through the air. Just as dropping a stone into a pond causes waves to spread out across the water, popping a balloon, vibrating a guitar string, or singing a song causes waves to spread through the air. When those waves hit our ear drums, we hear the sound. That means that the Whistle Stick must be producing waves in the air. But how? That is where the wooden spoon comes in. We will use it in place of the popsicle stick, and look at waves in water instead of air. Hold the wooden spoon between your palms, with the end of the spoon in a container of water.
Slide your palms to twirl the spoon slowly in the water. As the spoon spins, it makes waves in the water. Try spinning it at different speeds, noticing how that changes the distance between the waves. What you should notice is that as the spoon twirls, it pushes on the water to send out a wave. As you spin the spoon faster and faster, it makes more waves, and those waves get closer and closer together.
Now lets think about sound waves. The picture at the right shows a graph of the sound produced by the whistle stick. Notice that at the start of the sound, it reaches far up graph. The higher up the graph it goes, the closer together the sound waves are, and the higher the pitch of the sound. If you click the picture, you can watch a short video, letting you hear the sound, seeing how the changing sound matches the graph.
It is much easier to see (and hear) if we slow things down. This graph shows the same sound, stretched out four times longer than the original. That lets us see the curve as the pitch falls. Again, you can click the picture to watch a short video. Because it plays the sound slower, it is easier to see (and hear) that the sound begins with a high pitch (waves very close together), and then the pitch falls as the waves get farther apart.

Now lets put that all together. Like the wooden spoon, the faster the popsicle stick spins, the closer together the waves will be, and the higher the pitch of its sound. When you first snap your fingers, the Whistle Stick spins very fast, making a high pitched sound. As it pushes against the air to produce those waves, it gives up some of its energy of motion. That causes it to spin slower, producing a lower pitched sound. Looking at the graph, we can see that the rate of spin slows very quickly at first, and then more gradually.

If you remember from last week, I also made a Whistle Stick from a tongue depressor that was much wider. it made a much lower pitched sound, that did not last nearly as long. Why? The wider blade had to push against more air, transferring the energy of motion much faster, causing the speed of its spinning to drop much faster.

If you want to do some experimenting, you might try cutting notches into the sides of the stick or doing other things to change its shape. Do you think that would change the sound? Sounds like a good reason to eat more popsicles to me.